Growing solar PV energy generation must be coupled with low cost ... a low cost, efficient monitoring station for residential and low cost PV deployments.
Solar Irradiance, Wind and Temperature Monitoring for Residential PV Applications Muhammad Usama, Muhammad Nouman Qaiser and Hassan Abbas Khan Department Of Electrical Engineering, Lahore University of Management Sciences, Opposite Sector U, DHA, Lahore Cantt., 54792, Pakistan Abstract
-
Growing solar PV energy generation must be
coupled with low cost monitoring schemes for its wider uptake.
Conventional grid-tied PV systems, deployed generally in the developed
countries,
are
supplemented
with
However, emerging regions of Africa and South Asia require low local
monitoring for resource
optimization,
Conditioning
Panel
available through weather stations and other established means. cost
Signal
Solar
information
Block
preemptive
maintenance and accurate return-on-investment estimations. In this context, this paper proposes a design and implementation of
---------
t
f
----------------------
Main
Processor
---------------------------------,
a low cost, efficient monitoring station for residential and low cost PV deployments. The designed system included irradiance,
wind and temperature sensors coupling the output of a solar PV system for accurate energy estimations.
Index Terms
wind sensors.
-
Temperature
Wind Speed
Irradiance
Sensor
Sensor
Sensor
PV system, monitoring, irradiance sensors,
Fig. 1.
I.
INTRODUCTION
Increasing demand coupled with increasing cost of conventional thennal power generation has resulted in a shift towards renewables. In particular many emerging regions in Asia and Africa have seen a large interest in recent years due to a high solar potential coupled with falling prices of PV technology [ 1-4]. PV technology has therefore been growing in many countries with maturing technology for both off-grid and on-grid applications [2, 5, 6]. This has also lead to deployment of many small stand-alone PV systems used in conjunction with existing grid. Lucrative Feed-in-Tarrifs have also encouraged domestic consumer to invest in this technology to contribute towards sustainable electricity generation. Solar PV systems largely supplement grid or provide backup in case of grid outages. Frequently, real-time communication and control between the consumer and the utility is also achieved to allow utility and consumers to optimize power usage based on environmental, price preferences and technical issues of the system [7]. It is therefore pertinent to optimize the PV sizing of the system with effective monitoring of many important parameters such as irradiance, temperature and wind speed. These parameters dictate the energy yield from a system with insights into important perfonnance metrics. Usually, these parameters are
978-1-4799-7944-8/15/$31.00 ©2015 IEEE
Block
diagram
of
proposed
irradiance,
wind
and
temperature system.
monitored for high end applications. However, for smaller systems or low-end consumers, this monitoring system is absent to reduce the upfront cost. These installations generally rely on average data with low certainty and have no access to real-time input parameters. Thus, a need is felt for low cost and reliable solar parameter monitoring system that could provide a reasonable estimate of the perfonnance ration of a solar PV's installation with insights about real savings. Various parameters related to solar PV such as photo voltage and current from the panels, solar irradiance, panels' surface temperature and wind speed in the installation area must be continuously monitored. Voltage and current readings could be required for MPPT algorithm, while solar irradiance, temperature and wind speed generally help in gauging the perfonnance of the panels. A low cost and reliable implementation of these sensors will not only add to the efficient utilization but will also be useful to assess the trends in daily solar PV variation. This paper presents the design and implementation of a reliable and low cost implementation of sensors required for monitoring of various parameters associated with solar PV system. This is important in the energy assessment and remote energy monitoring of a PV system. The utility of such a monitoring system may also be extended to many other high end applications [8, 9].
,.....
I
-
Blades
RC
Filter
Tacho Generator
111
>....�"",.,........... AOC
Wind Fig. 2.
Design of low cost Wind Sensor. •
II. SYSTEM ARCHITECTURE The proposed monitoring system is divided into two modules. First module consists of parameter signal sensing/acquisition, conditioning, and digitization units. The latter module may display the data in various formats for consumer's disposal and may consist of a mobile phone application or other application. In this paper, we will focus mainly on the parameter sensing aspect for a monitoring system with a block diagram description of the system architecture presented in Fig. 1. A. Parameter Sensing
Accurate sensing of related parameters is a critical part of this work as it is imperative to come up with low cost techniques for sensing all the electrical as well as the related meteorological parameters which are necessary to optimize energy usage from grid and the local generation through solar PV. These critical parameters include; • Panel voltage at its optimum operating point • Panel current at its optimum operating point
40
-A- Ambient Temperattlre
35
15
10
7:00
8:00
9:00
10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Time of Day
Fig. 3.
Unity Gain Op-Amp
Measured module temperature significantly varies from the
ambient temperature.
978-1-4799-7944-8/15/$31.00 ©2015 IEEE
• • •
Current flowing into various loads as well as the battery backup, if any. Surface temperature of the panel(s) Wind speed Solar irradiance
1. Temperature and Wind Measurement Sensors
The performance of a solar PV system deteriorates with temperature. Solar panels are generally characterized at STC with requisite cell temperature at 25°C at lOOO W/m2 input irradiance [ 10]. This generally is not the case in field conditions, with higher temperatures not only leading to performance slumps but may also cause reliability issues. Therefore temperature monitoring of panels is important to assess the performance and flag any uncharacterized hotspots which may lead to a damage. It should also be noted that the cell temperature is generally higher than that of ambient temperature due to its enclosure in glass and tedlar to protect from environment. This increases the panel temperature and further loss in the output especially for warmer regions near equator. Therefore, for this work, solar panel's performance degradation can be estimated through temperature profile and direct measurement method is utilized for performance estimations. Low-cost LM35 is used for measurements of module temperature which is shown in Fig. 3 for a typical clear winter day. Wind speed affects a panel temperature by cooling effect through convection process. Higher the wind speed, higher will be the convection which will result in a lower panel temperature. Thus, wind speed is an important parameter and must be monitored especially for larger PV installations. We have analyzed wind speeds to ensure that this aspect is accounted for in energy predictions from the PV site. Wind speed sensor has been implemented using a 12V tacho generator. The AC output voltage of the generator is proportional to the wind speed which is rectified using full bridge rectifier circuit and subsequently filtered for noise
6-
1800
series resistance Rs, shunt resistance RSH and solar cell's ideality factor n to predict solar irradiance S as shown in ( 1)
1600 1400 1200
o
800
o o o
400
O�O Fig. 4.
VT=
o
600
200
( 1)
o
1000
(2)
nkT
Where, I is the measured short circuit current by setting V
0
0.2
q
--
0.4
Observed
0.6
0.8
1
1.2
1.4
Rectified Tacho-Generator Voltage [VI linear
relation
between
1.6
wind
1.8
speed
and
rectified tacho-generator voltage.
removal. The results obtained are shown in Fig. 4 which confirm the linear relation and hence enable accurate prediction of wind speed if the relation between tacho generator's RPM and wind speed becomes available. This rectified and filtered voltage is sensed using a simple resistor divider technique. This technique results relies on a simple low cost voltage sensor that can be built by readily available off the shelf components. This simple arrangement provides effective mechanism to monitor wind speed and is much cheaper than some of the alternative arrangements [ 1 112]. 2. 1rradiance Sensor
Solar irradiance monitoring is necessary to measure the performance ratio of the system along with monitoring long term performance of a PV system. Measurement of solar radiation intensity is carried out by high-end instruments or indirect costly methods (for example [ 13]) that use satellite based estimation of surface solar irradiance. In this work, we assess the solar irradiance using a test cell in short circuit mode. Estimation of solar irradiance using the short circuit current measurement has been carried out in an earlier [ 14] but it required estimation of inherent solar cell parameters like
equal to 0, 10 is reverse saturation current, lsc is the short circuit current at Standard Test Conditions, k is Boltzmann constant ( 1.38xlO-23 JK-1), q is the charge on an electron ( 1.6xl0-19 C), and T is the kelvin temperature of the pn junction. It is important to note that these inherent solar cell parameters vary from panel to panel. On the other hand, we used a 2W solar panel to measure the solar irradiance. A standard irradiance meter (thermopile pyranometer) has been used to calibrate the setup for the first time which has enabled close prediction of the available solar power with reasonable accuracy (maximum 7% error) as shown in Fig. 6. Another important aspect of the work is the use of low-cost Hall Effect sensor instead of a shunt resistance due to increased losses in the current path [ 15]. Accurate low loss current measurement is critical for efficient MPPT tracking as well as minimizing losses. Our design of solar irradiance sensor can be represented by (3) which stems from the theory that irradiance is directly proportional to short circuit current generated by a solar panel [ 16].
Irradiance = K(Ixa)
(3)
K represents
the equivalent gain of a subsequent amplifier and noise eliminating circuit whereas a is the sensitivity of the Hall Effect based current sensor which is typically 185 ± 5mV/A for± 5A range.
800
700
N�600
� �
s
~
Hall Effect
:.g
1::
500
400
based Current
300
Sensor 200 0900
Fig. 6.
1000
1100
1200
\300
Time of Day
1400
1500
1600
Predicted data fTom the designed sensor in comparison
with measurements from a high end commercial pyranomenter. Fig. 5.
Irradiance measurement setup.
978-1-4799-7944-8/15/$31.00 ©2015 IEEE
V.
CONCLUSION
The system based on our work presented in this paper is capable of temperature, wind speed and solar irradiance monitoring in an efficient, low cost and interactive way. This low-cost monitoring coupled with real-time performance characteristics of solar PV plant can be highly useful for through this could help preemptive maintenance of the system along with maximizing the performance ratio. The developed system is highly suitable for residential consumers and small & medium enterprises for optimum solar PV energy delivery to reduce the current energy crisis.
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Fig. 7.
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